Kanye West may have be this year's hottest hip-hop act - earning no fewer than eight Grammy nominations on Thursday - but he also sees himself as a political commentator.

Remember what he said during a national television fund-raiser for the victims of Hurricane Katrina. "Bush doesn't care about black people!" Blunt, certainly. But how you take West's wisdom about the current president may say something about how you respond to the notion, increasingly discussed, that hip-hop has become a new mainstream medium for political discourse, activism and change. And that it is a phenomenon not limited just to the United States.

On the contrary, hip-hop - the music genre that first emanated in the Jamaican, Puerto Rican and African American neighbourhoods of the Bronx in the 1970s and has since grown into a whole culture embracing fashion, its own slang and a style of dancing - may have become America's most potent and potentially most disruptive cultural export.

That hip-hop has attained a global reach is beyond much argument. Aimed essentially at a demographic spanning 13-34-year-olds, it transcends borders and religions. American soldiers listen to it in Iraq off duty. And so do Iraqi insurgents.

The statistics of the industry tell the story. By most recent estimates, global merchandising connected to hip-hop draws about $10bn (£5.7bn) a year from consumers, who number about 45 million. And, taken together, they have spending power of around $1 trillion. So says Forbes magazine anyway

Travel to almost any continent and you will hear the hip-hop sound, see the breakdancing on the streets and the rap fashions in the shops and markets. And you will hear the words - either from rap artists from America or sung by indigenous artists, such as Clotaire K in the Middle East or Disiz La Peste in France, who has risen to prominence recently with lyrics about decay and despair in the suburbs.

"For France it matters nothing what I do / In its mind I will always be / Just a youth from the banlieue," he sings in a recently recorded track.

Lacing popular songs with a political message is hardly novel. Listen to West's newest album, Late Registration - itself a reference to the need to get blacks into the voting booths - and you hear him riff about the black community being 'Merrill Lynched'. Yet, it is 65 years since Billie Holliday belted out Strange Fruit, a ballad decrying the actual lynching of blacks by whites in America.

West even takes on some of his peers' fascination with bling - the over-sized, over-priced jewellery that became the vulgar emblem of rap-star success - in another of his new tracks, Diamonds from Sierra Leone. Built around Shirley Bassey's Diamonds are Forever, it explores the links between the diamond trade and civil war, child soldiers and political upheaval on the African continent.

Nor is all this entirely new to hip-hop either. It was all the way back in 1989 that Public Enemy released the monster hit Fight the Power. "Our freedom of speech is freedom of death," they rapped. "We got to fight the power that be." Even then, it is sometimes argued, hip-hop was beginning to take the place of reggae and the music of protest.

Its impact on other countries is not always considered benign. In the civil war in Sierra Leone rebel army soldiers took to wearing T-shirts bearing the image of Tupac Shakur, the Los Angeles rap star whose fame only grew when he was murdered. The intrusion of hip-hop to the Arab music scene has angered some conservatives.

In the United States, however, political hip-hop is gradually become more than just a language of protest and rebellion. Some political scientists are urging politicians to take notice. As artists such as West, Eminem, Talib Kweli, Common and Nas increasingly infuse their tracks with socio-political rhetoric, progress is also bei

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